Arc initiator for plasma generator



United States Patent Office 32%,852 Patented Aug. 24, 1965 ARC INITIATOR FOR PLASMA GENERATOR Paul E. Martinson, Cleveland, Ohio, assignor to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio Filed Apr. 3, 1961, Ser. No. 100,112 9 Claims. (Cl. 3133'2) This invention relates to electric discharge apparatus and concerns particularly electrodes therefor.

The principal object of the invention is to provide an improved arc initiator or starting head for plasma stream apparatus.

An object of the invention is to provide simple, durable, reliable, relatively inexpensive methods and apparatus for initiating the plasma stream in a plasmatron without hazard to personnel or risk of damage to the apparatus.

A further object of the invention is to prolong the life of plasma stream apparatus and provide more efiicient or eliective cooling'means therefor.

Still another object of the invention is to provide a starting head with parts of prolonged life and in which parts worn after prolonged. use may be replaced readily without destruction of the remainder of the apparatus.

Other and further objects, features and advantages of the invention will become apparent as the description proceeds.

The plasmatron is a device which provides a means for utilizing, under close control, the extremely high temperature producing capacity of an electric are com- :bined with a flow of noble gas (or air) to provide a steady and continuous flame or plasm-ajet consisting of an electrically neutral inert gas which has been heated and highly ionized.

The plasma stream apparatus such as described more fully in Patents 2,922,869 and 2,929,952 to Giannini et -al., for example, includes a chamber, a front electrode or cathode, a back electrode or anode, a gas inlet orifice, and cooling means. Such apparatus provides the means of creating a source of temperature high enough to vaporize every known element and compound without destroying itself. The energy to create the high temperature is derived from an electrical discharge created and maintained between the front and back electrodes. The form and intensity of the arc is controlled by the electromagnetic forces and the dynamic forces created by the action of the gas within the chamber.

Owing to the high temperatures and currents involved and the nature of the radiation, safe guards for operating personnel are essential.

The general practice for starting the arc in such apparatus has been the shorting of the electrodes by means of a length of pencil leador approximately .075 inch diameter carbon rod inserted through an opening in the front electrode and making contact with both front and back electrodes. The carbon rod or pencil lead is held in a handle extension provided for this purpose when the apparatus has an open front.

A specific object of the invention is to provide for automatic or remote control of starting and to relieve the personnel of the hazard ofmanual manipulation and exposure to high current electrodes or the resultant high heat and hazardous radiation therefrom.

In carrying out the invention in accordance with a preferred form thereof, in a plasmatron having aback electrode mounted on a hollow cylindrical plasmatron head or electrode holder, the back electrode is provided with an eccentric opening in which-an auxiliary electrode is mounted. A lead wire is provided passing centrally through the electrode holder. The lead wire is surrounded by insulating tubing which in turn is surrounded :by thin metallic tubing such as a copper tube which is silver soldered to the auxiliary electrode opening in the back electrode to fill the opening and ground the metallic tube to the back electrode. A length of tungsten w re is soldered to the lead wire with a tip of tungsten wire flush with the surface of the back electrode and exposed.

A better understanding of the invention will be aiforded by the following detailed description considered in conjunction with the accompanying drawing in which FIG. 1 is a view of a longitudinal section, partly schematic, of an embodiment of the invention and FIG. 2 is an end view of the apparatus in FIG. 1.

The'invention is illustrated as employed in connection with the back electrode of a plasmatron in which the gas is injected spirally rather than centrally and utilizes, for example, a modification of the form of back electrode shown at 22 in Patent 2,929,952 or FIG. 8 of Patent 2,922,869.

As shown in FIG. 1 there is a back electrode 11 substantially in cup form secured in a suitable manner to a hollow cylindrical plasmatron head or electrode holder 12. The back electrode 11 has a conventional insert 13 composed of tungsten or other suitable refractory metal. In addition there is an exposed starting electrode 14 mounted in an eccentric opening 15 in the-face or top surface of the back electrode 11.

For supplying starting voltage to the auxiliary electrode 14 an auxiliary voltage source 16 is provided which is connected between the back electrode 11 and the auxiliary electrode 14. A lead wire 17 is provided, which is preferably composed of a corrosion resistant material such as nickel chromium alloy known as Nichrome, which will not melt at high voltage. The lead wire 17 is silversoldered at its upper end to the lower end of the tungsten wire electrode 14. A low-loss, high insulating-strength insulating tube 18 is provided composed of suitable material such as polytetrafluoroethylene, such as that sold under the trade name Teflon, for example. The Nichrome lead wire is stiff enough to that it can be pushed up through the insulating tube 18 and yet flexible to follow turns in'the tube 18. The insulating tube 18 is cut short at the end of the. lead wire 17 and extends upward half way into the opening 15 in the back electrode 11.

For protecting the insulation 18 and providing a grounded connection, a metallic sheath of flexible conducting material such as copper 19, for example, is prowided which also extends part way into the opening 15 in the back electrode 11 and is mechanically and electrically joined thereto'by means of a ring of silversolder 21. The tungsten wire auxiliary electrode 14 is supported and centered in the opening 15 by suitable insulating means such as a ceramic insulator 22 in the form of a bead. Preferably the opening 15 is countcrbored ,to receive the ceramic head 22. A rigid, secure auxiliaryelectrode assembly is accomplished by employing a refractory cement 23 of the type employed for coating high temperature electric heating wires, e.g., around the tungsten wire electrode 14, flush with the top surface of the back electrode 11. The cement 23 may be of any suitable composition which is insulating, non-corrosive and resistant to high temperature efiects. p

The assembly is arranged for circulating a suitable fluid coolant such as water throughthe interior 24 of the electrode holder 12 and the cavity 25 of the electrode 11. For this purpose a baffle 26 in hollow cylindrical form is provided preferably having a lower end portion 27 of reduced diameter. Suitable means are provided for securing the back electrode 11 to the electrode holder 12 with a gasketed or ground joint 28. For example, as schematically represented in FIG. 1, the lower edge of the back electrode 11 may be formed. with a lip 29 adapted to co-operate with shoulder 31 of an internally threaded sleeve 32 mating an annular nut 33.

The lower reduced diameter end portion 27 of the bafile 26 is externally threaded to receive a lock nut 34 for securing the bafile 26 to the electrode holder 12 and forming a seal at a ground or gasketed joint 35. The baffle 26 is formed with an opening 36 to which an inlet tube 37 is connected which passes through a suitable sealed opening in the electrode holder 12. On the opposite side, the electrode holder 12 is provided with an open ing 38 to which a coolant outlet tube 39 is connected. In this manner cooling water is caused to travel from the inlet tube 37 upward around the sheath 19 of the auxiliary electrode lead 17 into the cavity 25 of the back electrode 11 and brought downwards between the baffle 26 and the inner surface of the electrode holder 12, thence out through the outlet opening 38.

As shown the sheath 19 of the auxiliary electrode lead 1'7 passes down through the reduced diameter portion 27 of baflle 26 and a suitable seal is provided between the outer surface of the sheath 19 and the end of the bafile 26. To this end, for example, a gasket 41 may be provided with suitable compressing means such as a packing nut 42.

In thismanner a securely anchored auxiliary electrode may be provided for direct connection to the high voltage spark source 16. An efliciently operated water cooling system is provided which requires no elaborate leak sealing devices and no critical spacing. The sheath 19, for example, may take the form of eighth-inch copper tubing, providing ample clearance and passage-way for a cooling water stream of relatively wide cross-section, the outer diameter of the sheath 19 being no greater than one-third the inner diameter of the bafile 26, and the clearance between the outer surface of the bafile 26 and the inner surface of the electrode holder 12 being of the order of two-thirds that between the outer surface of the sheath 19 and the inner surface of the baflle 26.

Since the tungsten wire auxiliary electrode 14 is accurately and rigidly positioned, no problems of adjustment of gap spacing or burning away of the tungsten Wire are presented. Nevertheless, if adjustments or replacements should ever be required over a period of time, this can readily be done since merely a simple soldering operation is involved.

With the relatively great volume of water permitted to flow a relatively low temperature may be maintained in the entire electrode area. In the construction illustrated,

for example, approximately six gallons of water per minute may be caused to flow at 60 pounds per square inch pressure with the temperature difference between input and output water less than C. Consequently, very little maintenance, replacement and adjustment are required since the excessive heat generated by the arc is quickly carried away by the efficient cooling system.

While the invention has been described as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that the invention is not limited thereto, since various modifications will suggest themselves to those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1.-In a plasmatron, a back electrode, a longitudinally extending electrode holder, a hollow cylindrical baflle within the holder having an end adjacent the back electrode spaced from the electrode so as to provide an opening and having a second end sealed to the electrode holder, the baflle having a reduced diameter sealed end portion and having a coolant outlet opposite the inlet whereby coolant directed into the inlet is caused to pass longitudinally around the open end of the bafile against the electrode and in the opposite longitudinal direction through the outlet, the clearance between the baffie and the inner surface of the electrode holder being substantially greater than the thickness of the bafile, an auxiliary electrode mounted in the back electrode, insulated therefrom, and an auxiliary electrode lead sheath extending from the back electrode through the reduced diameter portion of the bafile whereby a sparking voltage connection may be made at the end of the sheath away from the back electrode where relatively low temperatures are encountered.

2. In combination a back electrode, a longitudinally extending electrode holder, a hollow cylindrical bafile within the holder having an end adjacent the back electrode spaced from the electrode so as to provide an opening and having a second end sealed to the electrode holder, the bafile having a fluid connection near the sealed end and the electrode holder having a fluid connection opposite the inlet, one connection serving as a coolant inlet and the other as a coolant outlet, whereby coolant directed into the inlet is caused to pass longitudinally around the open end of the bafile against the electrode and in the opposite longitudinal direction to the outlet, the clearance between the bafile and the inner surface of the electrode holder being substantially greater than the thick ness of the bafile, an auxiliary electrode mounted in the back electrode insulated therefrom and an auxiliary electrode lead sheath extending from the back electrode through the bafile with insulating means in the sheath whereby a sparking voltage connection may be made at the end of the sheath between the sheath and the lead away from the back electrode where relatively low temperatures are encountered.

3. In a plasmatron having a back electrode and a hollow electrode holder, an arc initiator comprising an auxiliary electrode composed of refractory metal mounted in said back electrode insulated therefrom, a sheath electrically and mechanically joined to the back electrode ex tending longitudinally through the interior of the electrode holder, and a high melting conductor extending through said sheath insulated therefrom electrically connected to said auxiliary electrode.

4. Apparatus as in claim 3, wherein the electrode holder is provided with an opening therein through which the sheath extends, and means for sealing the sheath in said opening.

5. A plasmatron arc initiator comprising in combination with a back electrode and a hollow cylindrical plasmatron head, said back electrode having an auxiliary electrode opening therein, a tubular baffie within the hollow cylindrical plasmatron head, the baffie having a lateral opening therein, a fluid coolant inlet tube connected to said bafile at said lateral opening, a lateral outlet in said head, whereby coolant traveling between the inlet tube and the outlet traverses the length of the baffie, the baffle having an end away from the back electrode with a clo sure to the hollow cylindrical head, a metallic tube joined to said back electrode around the opening therein, extending from said back electrode through the end of the baffle away from the back electrode, a seal between said baffle at said end and said metallic tube, an insulating tube in said metallic tube extending the length thereof, a lead wire extending through the insulating tube, a length of tungsten wire within the opening in said back electrode having an inner end silversoldered to said lead wire and an outer end with a tip flush with the surface of said back electrode to form an auxiliary electrode, a ceramic insulator bead surrounding said tungsten wire auxiliary electrode, and insulating, high-temperature-resistant cement filling the opening in the back electrode along the tungsten wire, the tungsten wire tip and the cement being flush with the surface of the back electrode, the bafiie having internal diameter approximately three times the external diameter of the metallic tube.

6. An are initiator for a plasmatron having a back electrode on a hollow cylindrical electrode holder, said back electrode having an auxiliary electrode opening therein, said are initiator comprising a grounding metallic tube mechanically and electrically joined to said back electrode around the opening therein, extending from said back electrode through the end of the electrode holder away from the back electrode, an insulating tube in said metallic tube extending the length thereof, a lead wire extending through the insulating tube, a length of refractory metal wire within the opening in said back electrode having an inner end silversoldered to said lead wire and an outer end with a tip flushed with the surface of said back electrode to form an auxiliary electrode, a ceramic insulator bead surrounding said tungsten wire auxiliary electrode, and insulating, high-temperature resistant cement filling the opening in the back electrode along the tungsten wire fiush with the surface of the back electrode.

'7. In a plasmatron having an arc initiator in a back electrode on a hollow cylindrical electrode holder, said back electrode having an auxiliary electrode opening therein for the arc initiator and having a surface with a refractory metal insert projecting therefrom, a tubular bafile within the hollow cylindrical electrode holder, the baflle having a lateral opening therein, a fluid coolant tube connected to said bafile at said lateral opening, a lateral opening in said electrode holder, a second tube connected thereto, whereby coolant traveling between the tubes traverses the length of the battle, the bafiie having an end away from the back electrode with a closure to the hollow cylindrical electrode holder, a metallic tube joined to said back electrode around the opening therein, extending from said back electrode through the end of the bafile away from the back electrode, a seal between said bafile at said end and said metallic tube, an insulating tube in said metallic tube extending the length thereof, a. lead wire extending through the insulating tube, a length of tungsten wire within the opening in said auxiliary electrode having an inner end silversoldered to said lead wire and an outer end with a tip flush with the surface of said back electrode to form an auxiliary electrode, the baflie having an internal diameter approximately three times the external diameter of the metallic tube, and a clearance between the external diameter of the bafile and the internal diameter of the hollow head being of the order of two-thirds the clearance between the external diameter of the metallic tube and the internal diameter of the bafile.

S. In a plasmatron having an arc initiator in a back electrode on a hollow cylindrical electrode holder, said back electrode having an auxiliary electrode opening therein for the arc initiator, a tubular baflle within the hollow cylindrical electrode holder, the baffle having a lateral opening therein, a fluid coolant tube connected to said baflle at said lateral opening, a lateral tube connected to said electrode holder, whereby coolant traveling between the tubes traverses the length of the baflle,

the baflle having an end away from the back electrode with a closure to the hollow cylindrical electrode holder, an arc initiator lead sheath extending from said back electrode opening through the end of the battle away from the back electrode, a seal between said bafile at said end and said sheath, the battle having an internal diameter approximately three times the external diameter of the metallic tube, and a clearance between the external diameter of the baffle and the internal diameter of the hollow head being of the order of two-thirds the clearance between the external diameter of the metallic tube and the internal diameter of the bafile.

9. A plasmatron arc initiator comprising in combination with a back electrode and a hollow cylindrical plasmatron head, said back electrode having an eccentric opening, an auxiliary electrode mounted in said opening, a tubular baflle within the hollow cylindrical plasmatron head, the bafile having a lateral opening therein, a fluid coolant inlet tube connected'to said bafile at said lateral opening, a lateral outlet in the said head, whereby coolant traveling between the inlet tube and the outlet traverses the length of the bafile, the baffle having an end away from the back electrode with a closure to the hollow cylindrical head and with a restricted opening, a copper tube joined to said head extending through said head from said back electrode through the restricted opening in said tubular baffle, a seal betweent said tubular bafiie at its restricted opening end and said copper tube, a tube of polytetrafluorethylene in said copper tube extending the length thereof, a Nichrome lead wire extending through the polytetrafluorethylene tube, said auxiliary electrode.

being composed of tungsten wire, silversoldered to said lead wire, a ceramic insulator bead surrounding said tungsten auxiliary electrode and refractory cement filling the opening in the back electrode around the tungsten wire flush with the surface of the back electrode, the wire having a tip flush with the said surface and exposed.

References Cited by the Examiner UNITED STATES PATENTS 2,053,327 9/36 Ehrke 31332 2,433,755 12/47 Haine et a1. 313-197 X 2,508,954 5/50 Latour et al 313-198 X 2,715,194 8/55 Combee et al. 313--32 3,114,077 12/63 Spindle 313-197 X FOREIGN PATENTS 825,899 12/59 Great Britain.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,202,852 August 24, 1965 Paul E. Martinson It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, lines 16, 29, 66 and 67, column 2, lines 14 and 21, column 3, line 64, column 4, lines 31, 44, 45 and 46, 48 and 72, column 5, lines 15 and 45, and column 6, lines 13, 14 and 15, and 17, for "plasmatron", each occurrence, read plasma stream apparatus Signed and sealed this 3rd day of January 1967.

( E Afloat:

W, SWIDER EDWARD J. BRENNER Officer Commissi ner of Patents 

1. IN A PLASMATRON, A BACK ELECTRODE, A LONGITUDINALLY EXTENDING ELECTRODE HOLDER, A HOLLOW CYLINDRICAL BAFFLE WITHIN THE HOLDER HAVING AN END ADJACENT THE BACK ELECTRODE SPACED FROM THE ELECTRODE SO AS TO PROVIDE AN OPENING AND HAVING A SECOND END SEALED TO THE ELECTRODE HOLDER, THE BAFFLE HAVING A REDUCED DIAMETER SEALED END PORTION AND HAVING A COOLANT OUTLET OPPOSITE THE INLET WHEREBY COOLANT DIRECTED INTO THE INLET IS CAUSED TO PASS LONGITUDINALLY AROUND THE OPEN END OF THE BAFFLE AGAINST THE ELECTRODE AND IN THE OPPOSITE LONGITUDINAL DIRECTION THROUGH THE OUTLET, THE CLEARANCE BETWEEN THE BAFFLE AND THE INNER SURFACE OF THE ELECTRODE HOLDER BEING SUBSTANTIALLY GREATER THAN THE THICKNESS OF THE BAFFLE, AN AUXILIARY ELECTRODE MOUNTED IN THE BACK ELECTRODE, INSULATED THEREFROM, AND AN AUXILIARY ELECTRODE LEAD SHEATH EXTENDING FROM THE BACK ELECTRODE THROUGH THE REDUCED DIAMETER PORTION OF THE BAFFLE WHEREBY A SPARKING VOLTAGE CONNECTION MAY BE MADE AT THE END OF THE SHEATH AWAY FROM THE BACK ELECTRODE WHERE RELATIVELY LOW TEMPERATURES ARE ENCOUNTERED. 